The present invention relates to contact structures in integrated circuits.
An electronic circuit is chemically and physically integrated into a substrate such as a silicon wafer by patterning regions in the substrate, and by patterning layers on the substrate. Patterning is generally done using well known photolithographic methods. These regions and layers can be conductive, for conductor and resistor fabrication, or insulative, for insulator and capacitor fabrication. They can also be of differing conductivity types, which is essential for transistor and diode fabrication. Degrees of resistance, capacitance, and conductivity are controllable, as are the physical dimensions and locations of the patterned regions and layers, making circuit integration possible.
Conductive layers (of metal such as aluminum, or of doped polycrystalline silicon, for example) are typically isolated from one another by a dielectric layer such as an oxide or nitride of silicon. It is often desirable to contact overlying metal to underlying polycrystalline silicon ("poly") or underlying substrate by etching a contact hole in the intervening dielectric and allowing the metal to flow into the hole during metal deposition. A contact to poly is called a "poly contact", and a contact to substrate is called a "substrate contact".